Souvenir/Event Photography and system for linking photos to website

I've been to a couple of events and places where I've seen people taking souvenir photos. A couple of the cameras that I remeber seeing had some sort of card reader attached. After taking your photo, the photographer hands you the card out of the card reader. This card has information about what website to go to for photos and includes a code so that you can get your photo.

What system is this? What equipment is used? How are the photos indexed to the cards/events/subjects? I've got a customer who wants to set something like this up for their events but doesn't want to use a service. All I can find after googling for a half hour is several photography services that do this, but nothing about the camera and equipment involved.

I know this question is a little vague, but part of the problem is that I don't quite have enough information to ask the right questions....